Re: [RFC PATCH v9 11/23] vhost: Move last chain id to SVQ element

[Jason Wang]

在 2022/7/7 02:39, Eugenio Pérez 写道:
> We will allow SVQ user to store opaque data for each element, so its
> easier if we store this kind of information just at avail.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>


Note that kernel driver doesn't have this optimization so far.  I wonder 
if this is not a must, let's post this on top of the shadow CVQ stuffs.

Thanks


> ---
>   hw/virtio/vhost-shadow-virtqueue.h |  3 +++
>   hw/virtio/vhost-shadow-virtqueue.c | 14 ++++++++------
>   2 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> b/hw/virtio/vhost-shadow-virtqueue.h
> index e434dc63b0..0e434e9fd0 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -17,6 +17,9 @@
>   
>   typedef struct SVQElement {
>       VirtQueueElement *elem;
> +
> +    /* Last descriptor of the chain */
> +    uint32_t last_chain_id;
>   } SVQElement;
>   
>   typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index cf1745fd4d..c5e49e51c5 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -239,7 +239,9 @@ static bool vhost_svq_add(VhostShadowVirtqueue *svq, const 
> struct iovec *out_sg,
>                             size_t out_num, const struct iovec *in_sg,
>                             size_t in_num, VirtQueueElement *elem)
>   {
> +    SVQElement *svq_elem;
>       unsigned qemu_head;
> +    size_t n;
>       bool ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num,
>                                     &qemu_head);
>       if (unlikely(!ok)) {
> @@ -247,7 +249,10 @@ static bool vhost_svq_add(VhostShadowVirtqueue *svq, const 
> struct iovec *out_sg,
>           return false;
>       }
>   
> -    svq->ring_id_maps[qemu_head].elem = elem;
> +    n = out_num + in_num;
> +    svq_elem = &svq->ring_id_maps[qemu_head];
> +    svq_elem->elem = elem;
> +    svq_elem->last_chain_id = vhost_svq_last_desc_of_chain(svq, n, qemu_head);
>       return true;
>   }
>   
> @@ -400,7 +405,7 @@ static SVQElement vhost_svq_get_buf(VhostShadowVirtqueue *svq, uint32_t *len)
>       const vring_used_t *used = svq->vring.used;
>       vring_used_elem_t used_elem;
>       SVQElement svq_elem = vhost_svq_empty_elem();
> -    uint16_t last_used, last_used_chain, num;
> +    uint16_t last_used;
>   
>       if (!vhost_svq_more_used(svq)) {
>           return svq_elem;
> @@ -428,11 +433,8 @@ static SVQElement vhost_svq_get_buf(VhostShadowVirtqueue 
> *svq, uint32_t *len)
>           return svq_elem;
>       }
>   
> -    num = svq_elem.elem->in_num + svq_elem.elem->out_num;
> -    last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
> -    svq->desc_next[last_used_chain] = svq->free_head;
> +    svq->desc_next[svq_elem.last_chain_id] = svq->free_head;
>       svq->free_head = used_elem.id;
> -
>       *len = used_elem.len;
>       return svq_elem;
>   }